Swap Graphics card with a new one, possible?!

-What kind of iMac I have:

iMac Intel 20" EMC 2266

-What I have in my iMac:

NVIDIA GeForce 9400 256 MB graphics

-Long story short:

Bought Mac (excited!)

Have had Mac around 3 years (loving it!)

Screen went black (slightly able to see it running with hand held light pointed at it!)

Tried resetting (SMC) 3 times (no go!)

Now using a used monitor next to it in mirroring mode (which is how I am here typing this out!)

Upon a lot of reading some say graphics card might have busted somehow or just backlight issue (hoping a disconnect wire could fix it!)

Never actually seen anywhere about the graphics card being replaced, with same graphics card of course (not possible to upgrade, I already know!)

PLEASE HELP :(